tools/memory-model: docs/references: Remove broken link to imgtec.com

MIPS documents are not provided at imgtec.com any more.
Get rid of useless link.

Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Acked-by: Andrea Parri <parri.andrea@gmail.com>

Author: akiyks

tools/memory-model/Documentation/references.txt

@@ -46,8 +46,7 @@ o	ARM Ltd. (Ed.). 2014. "ARM Architecture Reference Manual (ARMv8,
 
 o	Imagination Technologies, LTD. 2015. "MIPS(R) Architecture
 	For Programmers, Volume II-A: The MIPS64(R) Instruction,
-	Set Reference Manual". Imagination Technologies,
-	LTD. https://imgtec.com/?do-download=4302.
+	Set Reference Manual". Imagination Technologies, LTD.
 
 o	Shaked Flur, Kathryn E. Gray, Christopher Pulte, Susmit
 	Sarkar, Ali Sezgin, Luc Maranget, Will Deacon, and Peter